The invention relates to a fluid friction clutch, especially a cooling fan for an internal combustion engine.
From German Publ. Spec. No. 2,803,975 a cooling fan for an internal combustion engine is known, the fluid friction clutch or viscous clutch of which comprises a housing carrying the fan blades and a runner or rotor arranged in a working chamber of the housing and driven by the internal combustion engine. The housing and the rotor are rotatable in relation to one another and form a shear gap by way of which, when it is filled with a viscous shear fluid, the torque is transmitted from the rotor to the housing and thus the fan blades. In the region of the external circumference of the rotor a pump device is provided which, in relative rotation of the rotor and the housing, delivers the shear fluid out of the working chamber into a reservoir, likewise formed by the housing. A temperature-controlled valve controls the return flow of the shear fluid from the reservoir back into the working chamber.
The shear gap of the known fluid friction clutch has a serpentine form, to increase the torque-transmitting areas, and is formed by circular ribs of the rotor and of the housing, which ribs are arranged coaxially one within the other. The ribs have cylindrical peripheral surfaces and extend each axially between the ribs of the other part. In this way the object is achieved that despite comparatively small dimensions a comparatively great torque can be transmitted. Admittedly in the torque transmission heat of friction occurs which, in the known fluid friction clutch, cannot in all operational situations be conducted away quickly enough, so that the shear fluid situated in the shear gaps is strongly heated. This leads to a distinct reduction of the maximum transmittable torque and to a thermal overloading of the shear fluid, considerably shortening its life.
Now the invention provides a fluid friction clutch which firstly, with comparatively small dimensions, can transmit a comparatively great torque, in such a manner that heat generated in the shear gap can be conducted away well. Despite these properties the fluid friction clutch is simple to produce.